Ancient Aliens - Unerklärliche Phänomene

Legends existed in China about dragons? Must've been aliens.

Mayans thought there were Gods who could influence the weather? Aliens.

Primitive cave paintings resembling weird looking humans? Aliens.

I don't necessarily think that the ancient astronaut theory is totally ludicrous, but the evidence provided by "experts" in this show is lacking, and almost entirely driven by conformation bias. They have already drawn their conclusion (aliens), and work their way backwards from there.

That said, you'll probably learn some interesting things about the past, and the idea itself is, at least for me, quite thought provoking.